Oil dash-pot



G. A. BURN'HAM.

OIL DASH POT.

APPLICATION FILED Inn II.- I917.

Patented Dec. 20, 1921.

UNITED STATES PATENT OFFICE.

GEORGE A. BURNHAM, OF SAUGUS, MASSACHUSETTS, ASSIGNOR TO SEARS B.CONDIT,

JR., OF BBOOKLINE, MASSACHUSETTS.

OIL DASH-POT.

Specification of Letters Patent.

Patented Dec. 20, 1921.

To all whom it may concern:

Be it known that I, GEORGE A. BURNHAM, a citizen of the United States,residing at Saugus, in the county of Essex and State of Massachusetts,have invented an Improvement in Oil Dash-Pots, of which the following isa specification.

My invention relates to time limit relays of the type in which an oildash-pot is used to retard the motion of the core, the rate of leakageof oil by the plunger determining the time interval between theoccurrence of the overload and the operation of the relay switch.

When an oil dash-pot time limit relay is operated under severeoverloads, there is a pumping action set up which tends to eject oilaround the stem of the plunger rod. Each action of the relay diminishesby a small amount the quantity of oil in the dashpot or cylinder, andeventually the action of the relay becomes irregular and performs as anordinary circuit breaker, the gradual loss of oil destroying the timelimit features.

Consequently, an object of my invention is to provide means whereby thisobjectionable operation and loss of oil is prevented, and the relaythereby continually maintained in operating order. I

The means by which this object is attained is to maintain a body of oilin a suitable container, at such a height above the opening into thedash-pot that the energy of the stream of oil issuing from the openingof the dash-pot during pumping action of the piston is expended increating eddy currents in the body of oil, to such an extent that theremaining energy in the stream, due to its velocity, is insuflicient toovercome the surface tension of the body of oil abovethe dash-pot andbreak through the surface of the oil and escape from the cylinder as ajet.

A further object of my invention is in the provision of a relay having asuitable receptacle for the dash pot to serve as a container for the oilfor the purpose above set forth.

Figure 1 shows a front elevation, partly in section, of an oil dash-pottime limit relay embodying my invention.

Fig. 2 is a sectional elevation of Fig. 1 along line 2-2.

Fig. 3 is a sectional plan view of Fig. 1 along line 33.

Fig. 4 is an elevation of the oil retainer.

Fig. 5 illustrates a modified form of my invention.

As here shown, the oil dash-pot time limit relay comprises the core 10operable within the coil or solenoid 11 which is inclosed in a case12'adapted to be secured to a base or panel 12. The upper part of core10 is adapted to engage contacts (not shown), at some predetermined timeafter the occurrence of an overload, to control a suitable circuit. Arod 13 depends from the lower end of plunger on core 10 and terminatesin a piston 14 which is inclosed in a cylinder or dash-pot 15. Cylinder15 is secured, by screw threads, to a slotted tube 17 depending from thesolenoid 11 and concentric with core 10 and piston let.

Bushing 16 is secured in the end of tube 17 adjacent the cylinder 15,and has a concentrically located opening 16 for the passage of pistonrod 13 therethrough. Rod 13, attached to piston 14 is adjustable inplunger 10 to vary the load at which the relay will operate and isprovided intermediate its length, with a knurled nut 18 fixed to pistonrod 13. Nut 18 is of smaller diameter than the inner diameter of saidtube 17 and in the lowest position of plunger 10 and piston 14., ismoved downward with said piston to engage bushing 16 to thereby limitthe downward movement of piston 14 and plunger 10.

A casing 19 is provided to inclose the cylinder 15 and allied parts, andhas compartments 20 in which cylinders 15 are disposed whichcompartments are adapted to contain oil. Casing 19 is attached tosolenoid inclosing case 12 by a wing nut and threaded rod.

In the modified form of oil dash-pot time limit relay embodying myinvention, as

illustrated in Fig. 5, wherein a solenoid and dash-pot are combined asan independent unit, an individual casing 21 is provided for eachdash-pot, to maintain the oil level above the opening into the dash-pot.

In the operation of the usual type of oil dash-pot time limit relay, thepiston 14 nor mally occupies a position at the bottom of the dash-pot orcylinder 15, and a column of oil is maintained above the piston to somelevel as aa, Fig. 2. With a current flow in solenoid 11 in a normalexcess of that for which the plunger 10 is set, plunger 10 is drawnwithin solenoid 11 and raises piston l h'creati'ng a partial vacuumbetween the under side of piston 14 and cylinder 15. Due to thedifference of pressure existing between the opposite sides of thepiston, oil is forced between the piston and the cylinder to fill thespace beneath the piston, and the piston" and cylinder are made of suchdiameter that a suitable leakage may take place therebetween. Iftheoverload is moderate, the rate at whichthe piston 14 is raised incylinder 15 is approximately equal to-the rate of flow of oil betweenthe piston and cylinder and consequently the .oil in the dash-pot abovethe piston is maintained at. a substantially constant level.

lVith a very heavy load, however, the rate of upward movement. of piston14 becomes much greater than the rate-of downward flow of oil around-thepiston and consequently the oil level in the cylinder or dash-pot 15 israised, and a pumping action takes place,

which results in a spurt of oil through the opening 16, and theconsequent loss of the oil. Every operation of the relay under heavyoverload results in an additional loss of oil until finally, due toinsufficient oil supply, occasioned by the loss of oil, the action ofthe relay becomes erratic, and soon functions only as a circuit breaker.

The pumping action of the oil dash-pot of time limit relay is inherentto the design of the'apparatus, and can not be obviated.

. In the operation of a relay embodying my invention, the compartment 20surrounding dash-pot 15 is filled withoil to such a level that whenthedash-pot is disposed within the compartment, the oil level willassume some level 72-73, Fig. 2, substantiallyv above the opening 16'communicating with the dashpot 1'5.

The operatlon of the relay with the oil at this level bb, for smallcurrent overloads, and consequently but slight pumping action, issubstantially the same as in the ordi'nary type of oil dash-pot relay,the operation of which has been previously explained.

. Under heavy overloads, and strong pumping action, however, theoperation is materially different. When the piston is raised under heavyoverload, and pumping action. occurs, a flow of oil is set up throughopening 16' of cylinder 15, as in the ordinarytype of oil dash-potrelay. This stream of 011 has cons derable velocity when it issues fromopening 16', and in the ordinary relay,

1,eOO,863

is thrown from the dash-pot and lost. In the apparatus embodying myinvention, however, this stream, flowing at comparatively high velocity,enters the body ofoil maintained in compartment 20 above opening 16.This body of oil serves to absorb the velocity of the stream by causingit to set up eddy currents inthe body of oil to such an extent that whenthe stream reaches the top surface 6-1), the pressure due to itsvelocity is insuflicient to overcome the surface tension of the oil andbreak-through thesurface, and consequently no spurt or jet of oilescapes from the apparatus.

The oil level bb must be initially of such a height above the opening 16that, under excessive overloads, the velocity of the oil stream issuingfrom said opening will be absorbed by the oil above the opening to sucha degree that the pressure of the oil jet, due

to its remaining velocity, isbelow that necan inclosing'casing' for saidcylinder adapted toreceive oil.

'2. A retardation device comprising a solenoid, an inclosing casingtherefor, a core operable within said solenoid, a dash pot comprising acylinder adapted to contain oil dependlng from. said solenoid, a pistonop erable therein, a piston-rod connected with said piston extendedthrough the end of said cylinder and connected with said core, and aninclosing casing for said cylinder adapted to'receive oil havingmeans'for'detachably securing it to'the solenoid inclosing casing.

In testimony whereof, I have signed my name to this specification, inthe presence of two subscribing witnesses.

' GEORGE A. BURNHAM.

Witnesses:

T. T. GREENWQOI ,H. B. DAvis.

